The present invention relates to a robot control apparatus having a function to smoothly stop the robot arm at a time of emergency stop.
In general, there are provided in robots a position detector for detecting the position of an actuation unit and a speed detector for detecting a speed of a motor which drives the actuation unit. A position control unit constituting the robot control apparatus produces a speed reference on the basis of a deviation between a predetermined movement value and a position detection value. Thus, the speed control unit produces a torque reference on the basis of a deviation between this speed reference and a speed detection value. The motor for actuating the robot is subjected to current control on the basis of the torque reference thus produced.
In the event that an abnormal condition occurs in the robot, it is required to conduct emergency stop. In this case, a command for allowing the speed reference to be forcedly equal to zero is produced. However, when such a step-like-change occurs in the speed reference, the torque reference also abruptly varies. As a result, vibration will occur until the actuation unit of the robot is completely stopped. Particularly, according as robots become large-sized in recent years, there is a tendency that robots of lower rigidity are employed. Under these circumstances, such a vibration of the actuation unit results in the problem that work is dropped off or the actuation unit is broken. While such a vibration can be prevented by preparing a program such that the speed reference is smoothly changed to zero, it is not preferable to take a countermeasure for occurrence of abnormal conditions using a program because safety is injured. Accordingly, it is inevitable to cause the speed reference to be forcedly equal to zero for carrying out emergency stop in safety. For this reason, vibration of the robot actuation unit at the time of emergency stop has become serious problem in the art.